1. Field of the Invention
The present invention relates to a counterweight attaching and detaching apparatus for a crane that attaches and detaches a counterweight to and from an upper rotating body by itself.
2. Description of the Related Art
A large crawler crane is difficult to transport. Therefore, the crawler crane is disassembled into a plurality of blocks, and the blocks are transported by a trailer, and are assembled into the crane at a worksite. The crawler crane attaches and detaches a counterweight by itself by using a boom raising device when other cranes are unavailable.
A counterweight attaching and detaching apparatus and a method using the apparatus disclosed in the related art will be described, with reference to FIGS. 7 to 10, for comparison with the present invention.
The distance L between the peak of a gantry 11 suspending weights 5 to 8, and the upper surfaces of the weights 5 to 8 shown in FIG. 8 (hereinafter sometimes referred to as a “peak-to-weight distance”) varies depending on the positions of the weights 5 to 8 in the front-rear direction. Therefore, there is a need to adjust the length of a suspension member 15 in accordance with the variation.
In this case, since the length cannot be sufficiently adjusted only by extension and contraction of a hydraulic cylinder 16, it is also adjusted by selectively using a link 18, a link 19, and a link 20.
The adjustment will now be described more specifically:
(i) When the first weight 5 that has the longest distance L is attached or detached, all the links 18 to 20 are connected in series to make the length of the suspension member 15 the largest (the left state in FIG. 9).
(ii) When the second and third weights 6 and 7 are attached or detached, the link 18 is removed, and the other links 19 and 20 are used (the right state in FIG. 9 and the left state in FIG. 10). In this case, the difference in length L between the weights 6 and 7 is overcome by extension and contraction of the hydraulic cylinder 16.
(iii) When the fourth weight 8 that has the shortest distance L is attached or detached, the link 20 is removed, and only the link 19 is used to make the length of the suspension member 15 the smallest (the right state in FIG. 10).
The lower end of the suspension member 15 is fastened to any of rings 21 to 24 protruding from the upper surfaces of the weights 5 to 8, and the weights 5 to 8 are moved up and down between the ground and the mounting positions by raising and lowering the gantry 11.
The amounts A of protrusion of the rings 21 to 24 (represented by the amount of protrusion of the centers of holes for a pin that fastens the lower end of the suspension member 15 in FIG. 8) of the weights 5 to 8 are equally set. Since the length of the suspension member 15 is adjusted only by the links 18 to 20 in order to cope with the variation of the peak-to-weight distance L, the links 18 to 20 need to be selectively used correspondingly to the weights 5 to 8.
That is, the long and heavy links 18 and 20 must be removed or connected during three operations of attaching or detaching the weight 5, the weights 6 and 7, and the weight 8, and the operations are interrupted. Therefore, the operation efficiency is seriously decreased.
It is conceivable to adjust the length only by a long hydraulic cylinder without using a link, as disclosed in Japanese Registered Utility Model No. 2542385. However, except when the counterweight is attached or detached, the long cylinder is obstructive (for example, it must be shifted when folding the gantry). This is a practical problem.
Although it is also conceivable to use a multiple stroke cylinder that shortens to a small size, this is disadvantageous in cost.